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Old 6th January 2009, 06:05 PM   #11
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You should be fine with that. The 20mA that the front end current source is supplying, is split between two fets. If you want to be perfect, match each at 10mA.




question for all: While running below the optimum 25V, say 10-15V rails, couldn't you just increase diff pair bias to make up for output stage gate capacitance issues?
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Old 6th January 2009, 10:05 PM   #12
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Given that 10mA per device is easy to achieve (it's not like you're trying to do whole amps for output devices), I'd say match them at 10mA.
The problem with the capacitance is not just the amount, but the fact that it's non-linear with the voltage across the device...and what fun is a device that can't wiggle with the volts? Music will come out, and depending on your standards you might just be really happy, but it won't be as good as it could be.

Grey
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Old 7th January 2009, 07:06 PM   #13
tpsorin is offline tpsorin  Romania
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OK. Thanks.
I did matching at 10mA.

Another 2 questions:
- Is there any difference in sound between 1 IRF644 biased at 1A and 2 parallel biased at 0.5A each? I think power dissipation is better with 2 parallel devices. I have one heatsink of 8x25x5cm for each channel.

- Shall I make stabilized power supply? Or a simple C-R-C is enough?
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Old 7th January 2009, 07:39 PM   #14
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by tpsorin
OK. Thanks.
I did matching at 10mA.

Another 2 questions:
- Is there any difference in sound between 1 IRF644 biased at 1A and 2 parallel biased at 0.5A each? I think power dissipation is better with 2 parallel devices. I have one heatsink of 8x25x5cm for each channel.

- Shall I make stabilized power supply? Or a simple C-R-C is enough?

if you use proper h'sinking , with one at 1A - it will be just on right temp

simple CRC is good enough , if you have enough C

anyway - I prefer CLC , and plain cap multiplier , over regulated PSU , if CMRR of stage itself permit that ;
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Old 7th January 2009, 07:47 PM   #15
Magura is offline Magura  Denmark
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Quote:
Originally posted by Zen Mod


anyway - I prefer CLC , and plain cap multiplier , over regulated PSU , if CMRR of stage itself permit that ;

CLC is mostly king, when feeding a power amp. Get yourself a pair of respectable 2mH air core inductors, and you're sure fine.


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Old 7th January 2009, 11:22 PM   #16
Bengali is offline Bengali  United States
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Default brian gt aleph psu board

Hi,

for the brian gt mini-Aleph PSU boards, he mentions if using 4pin capacitors, some of the pins need to be clipped or they will short.

is clipping the pins enough or the pads on the pcb itself also need to be isolated(tape)?

thx
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Old 17th February 2009, 07:50 PM   #17
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Hi !
I'm building a standard Mini-A using BrianGT's boards (Amp+PSU) with a 2x12V toroid, hoping 15v at the rails. I need about 10W.

I was wondering about some questions :
1 - With 3K3 resistors as R1/R2, a strap is required for R3 and R12. Please confirm.
2 - Could the PSU board be fed with 2 Leds and a single 10K R ? Please confirm.
3 - I'm planning to use 2x(22000F/10000F/3K3/10000F) in this order. I'm right or not ?
Would it be a better solution with 22000F/22000F/3K3/10000F ?

Nice to read from the expert !
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Old 17th February 2009, 09:01 PM   #18
CfM is offline CfM  Germany
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Quote:
Originally posted by korben69
I'm building a standard Mini-A using BrianGT's boards (Amp+PSU) with a 2x12V toroid, hoping 15v at the rails. I need about 10W.

I was wondering about some questions :
1 - With 3K3 resistors as R1/R2, a strap is required for R3 and R12. Please confirm.
2 - Could the PSU board be fed with 2 Leds and a single 10K R ? Please confirm.
3 - I'm planning to use 2x(22000F/10000F/3K3/10000F) in this order. I'm right or not ?
Would it be a better solution with 22000F/22000F/3K3/10000F ?
Hi Korben,

R1/R2 and R3-R12 are independent from each other. R1/R2 are the bleeding resistors, the latter are the filter resistors. I would put in some small resistors there, if you don't want to waste too much voltage even 0.22 Ohm will do better then no resistors at all.
You should get Duncan's PSU Designer, then you can see, which capacitor arrangement suits best.

Greetings,
Chris
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Old 17th February 2009, 10:30 PM   #19
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Thanks CfM !
I'll try with lower values, maybe 0.47R or .22R if I've got them...
Do you have an opinion about caps values ?
Regards
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Old 20th April 2009, 06:14 PM   #20
Beftus is offline Beftus  Netherlands
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Sorry for cross posting this but I realised this may be a far better place for answers & opinions, so please bear with me.

I'm gonna make a mini-A using BrianGT's PCBs and I'm planning on using 10,000uF/10,000uF/R33/10,000uF for the psu. I'm gonna make the R33 using three 1R wirewounds in parallel.
1. Are wirewounds OK for this? Will the inductance affect the RC filter time-constant?

For rectifier diodes I wanna use four HFA08TB60's.
2. Should I go for diodes that can handle more current?

I was thinking about using a 225VA toroid.
3. Will 225VA be enough or should I buy 300VA?
4. 2x12V or 2x15V?

I have difficulty in sourcing the 3 ohm resistors (R0) for the amp pcb's. A value of 3 ohm apparently is an American value. In Europe it's either 2R7 or 3R3. How critical is the value of R0?
5. Could 2R7 or 3R3 work too?
6. How 'bout creating ~3 ohm with a 5R6 and a 6R8 in parallel?

Thanks!
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